Charter Oak is located in the eastern San Gabriel Valley, situated along Arrow Highway in between Covina to the south and Glendora to the north. Some residents refer to it as the "unincorporated part of Covina," though a large portion of Charter Oak is in Glendora.
Originally a small agricultural town (primarily citrus orchards) centered around the intersection of Arrow Highway and Bonnie Cove Avenue, population growth greatly expanded the area recognized as "Charter Oak". Since the 1960s, it has been known as a "bedroom community" suburb of Los Angeles and commercial agriculture is nearly gone.
Today, the generally-accepted boundaries of Charter Oak are I-210 to the north, Lone Hill Avenue to the east, Puente Avenue to the south and Grand Avenue to the west. In the mid-1960s, Glendora annexed the area north of Arrow Highway and Covina annexed the area south of Arrow Highway. Several small "county islands" of unincorporated area remained within Charter Oak until the 1980s.
As of the census of 2000, there were 9,027 people, 3,048 households, and 2,255 families residing in the CDP. The population density was 3,747.7/km² (9,711.3/mi²). There were 3,115 housing units at an average density of 1,293.2/km² (3,351.1/mi²). The racial makeup of the CDP was 65.30% White, 4.77% Black or African American, 1.27% Native American, 9.19% Asian, 0.14% Pacific Islander, 14.02% from other races, and 5.28% from two or more races. 36.58% of the population were Hispanic or Latino of any race.
There were 3,048 households out of which 40.8% had children under the age of 18 living with them, 50.2% were married couples living together, 18.1% had a female householder with no husband present, and 26.0% were non-families. 19.8% of all households were made up of individuals and 6.6% had someone living alone who was 65 years of age or older. The average household size was 2.95 and the average family size was 3.41.
In the CDP the population was spread out with 29.6% under the age of 18, 9.4% from 18 to 24, 32.1% from 25 to 44, 20.6% from 45 to 64, and 8.3% who were 65 years of age or older. The median age was 33 years. For every 100 females there were 95.3 males. For every 100 females age 18 and over, there were 91.1 males.
The median income for a household in the CDP was $50,744, and the median income for a family was $55,294. Males had a median income of $37,153 versus $30,703 for females. The per capita income for the CDP was $18,766. About 5.9% of families and 7.5% of the population were below the poverty line, including 9.4% of those under age 18 and 7.5% of those age 65 or over.